Some petroleum fractions, particularly middle distillate petroleum fuels and dark oils typically contain varying quantities of dissolved wax. Waxes are hydrocarbons of high molecular weight which are solids at about 70.degree. F. or less such as paraffin and microcrystalline. Wax has a tendency to crystallize within a petroleum fraction as the petroleum fraction temperature decreases. Crystallized wax causes the petroleum fraction to cloud, become viscous and, as the temperature drops, to solidify. A particular problem exists during the winter months when wax crystallization caused by low outdoor temperatures can cause fuel lines, filters and the like to clog in diesel engines and furnaces which burn petroleum fractions.
Pour point depressants such as kerosene and polymerized higher esters of acrylic acid derivatives are well known in the art. When added to a petroleum fraction, pour point depressants lower the cloud point and the pour point temperature of the petroleum fraction. Kerosene is also used as a diluent to lower the cloud point of petroleum fractions. However, wax content within a petroleum fraction often varies with the distillation conditions under which the fraction was produced and with the source of crude oil from which the fraction was distilled. Thus, the amount of pour point depressant needed to achieve a desired pour point in a petroleum fraction will vary.
Standard tests have been developed by the American Society for Testing and Materials (ASTM) to determine cloud and pour point temperatures. The cloud point temperature test, ASTM D2300-91, determines the temperature at which a cloud of wax crystals will form in a volume of petroleum product. The pour point temperature test ASTM D97-87 determines the lowest temperature at which a petroleum product will flow. Both ASTM D2500-91 and D97-87 are manual tests which require hands on manipulation of petroleum product samples to determine cloud and pour point temperatures.
To account for weather extremes, it is generally desirable to utilize fuels (petroleum fractions) having pour points at least about 10-15.degree. F. below the anticipated operating temperature of a fuel. To depress the cloud and pour point temperatures of fuels to a desired temperature it is common practice to remove a sample of fuel from a refinery production stream, add a pour point depressant to the fuel sample, conduct ASTM's D97-87 and D2500-91 to determine the pour point depressant's effect on the sample and to repeat these steps until addition of pour point depressant results in desired cloud and pour point temperatures in the sample. A proportional amount of pour point depressant is then injected into the process stream to lower the pour point of the fuel before it is shipped for use. Since ASTM's D97-87 and D2500-91 are manual tests this process is very time consuming.
Attempts have been made to eliminate the manual determination of cloud and pour point temperatures. An apparatus utilizing a microprocessor controlled photocell is available commercially from Precision Scientific, Inc. of Chicago, Ill., which determines the cloud point temperature of a material. A separate apparatus utilizing air pressure pulses to determine pour point temperature is also available commercially from Precision Scientific, Inc. Alcor Engineering manufactures a pour point tester utilizing a weighted ring which is visually monitored for cessation of movement by the tester user to determine the pour point temperature of a material. However, a single unitary apparatus is not currently available to determine both cloud and pour point temperatures of a material.
Therefore, a need exists for an apparatus and a method for using the apparatus to automatically determining cloud and pour point temperatures of petroleum fractions. A need also exists for an apparatus which can be utilized on line with an automatic chemical feed system to depress the cloud and pour point temperatures of petroleum fractions as they are processed.
It is an object of this invention to provide an apparatus and a method of using the apparatus to automatically determine both cloud and pour point temperatures of a petroleum fraction. It is also an object of this invention to provide an apparatus which can be installed on-line with a petroleum fraction production stream to automatically determine cloud and pour point temperatures of a petroleum fraction taken from the production stream. It is yet another object of this invention to provide an apparatus and a method of using the apparatus to automatically depress the cloud and pour point temperatures of a petroleum fraction to temperatures less than or equal to predetermined temperatures.